In court papers, federal prosecutors have said groups of Proud Boys also coordinated travel to Washington and shared lodging near the city, with the intent of disrupting Congress and advancing Mr. Trump’s efforts to unlawfully maintain his grip on the presidency.
The communication between the person associated with the White House and the member of the Proud Boys was discovered in part through data that the F.B.I. obtained from technology and telecommunications companies immediately after the assault.
Court documents show F.B.I. warrants for a list of all the phones associated with the cell towers serving the Capitol, and that it received information from the major cellphone carriers on the numbers called by everyone on the Capitol’s cell towers during the riot, three officials familiar with the investigation said.
The F.B.I. also obtained a “geofence” warrant for all the Android devices that Google recorded within the building during the assault, the officials said. A geofence warrant legally gives law enforcement a list of mobile devices that are able to be identified within a particular geographic area. Jill Sanborn, the head of counterterrorism at the F.B.I., testified before a Senate panel on Wednesday that all the data the F.B.I. had gathered in its investigation into the riot was obtained legally through subpoenas and search warrants.
Although investigators have found no contact between the rioters and members of Congress during the attack, those records have shown evidence in the days leading up to Jan. 6 of communications between far-right extremists and lawmakers who were planning to appear at the rally featuring Mr. Trump that occurred just before the assault, according to one of the officials.
The Justice Department is examining those communications, but it has not opened investigations into any members, the official said. A department spokesman declined to comment.
The F.B.I. did, however, say on Thursday that it had arrested a former State Department aide on charges related to the attack, including unlawful entry, violent and disorderly conduct, obstructing Congress and law enforcement, and assaulting an officer with a dangerous weapon.